Convective flow in the deep mantle controls Earth's dynamic evolution, influences plate tectonics, and has shaped Earth's current surface features. Present and past convection-induced deformation manifests itself in seismic anisotropy, which is particularly strong in the mantle's uppermost and lowermost portions. While the general patterns of seismic anisotropy have been mapped for the upper mantle, anisotropy in the lowermost mantle (called D′′) is at an earlier stage of exploration. Here we review recent progress in methods to measure and interpret D′′ anisotropy. Our understanding of the limitations of existing methods and the development of new measurement strategies have been aided enormously by the availability of high-performance computing resources. We give an overview of how measurements of seismic anisotropy can help constrain the mineralogy and fabric of the deep mantle. Specifically, new and creative strategies that combine multiple types of observations provide much tighter constraints on the geometry of anisotropy than have previously been possible. We also discuss how deep mantle seismic anisotropy provides insights into lowermost mantle dynamics. We summarize what we have learned so far from measurements of D′′ anisotropy, how inferences of lowermost mantle flow from measurements of seismic anisotropy relate to geodynamic models of mantle flow, and what challenges we face going forward. Finally, we discuss some of the important unsolved problems related to the dynamics of the lowermost mantle that can be elucidated in the future by combining observations of seismic anisotropy with geodynamic predictions of lowermost mantle flow.

中文翻译：

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利用地震各向异性观测绘制最低地幔对流图的进展

地幔深处的对流控制着地球的动态演化，影响板块构造，并塑造了地球目前的表面特征。当前和过去的对流引起的变形表现为地震各向异性，这种各向异性在地幔的最上部和最下部部分尤其强烈。虽然上地幔地震各向异性的一般模式已经绘制出来，但最下地幔（称为 D''）的各向异性仍处于勘探的早期阶段。在这里，我们回顾了测量和解释 D′′ 各向异性的方法的最新进展。高性能计算资源的可用性极大地帮助了我们对现有方法局限性的理解和新测量策略的开发。我们概述了地震各向异性的测量如何帮助限制深部地幔的矿物学和结构。具体来说，结合多种类型观察的新的和创造性的策略对各向异性的几何形状提供了比以前更严格的限制。我们还讨论了深部地幔地震各向异性如何提供对最低地幔动力学的见解。我们总结了迄今为止从 D′′ 各向异性测量中学到的知识，根据地震各向异性测量得出的最低地幔流的推论如何与地幔流的地球动力学模型相关，以及我们未来面临的挑战。最后，我们讨论了与最低地幔动力学相关的一些重要的未解决问题，这些问题可以在未来通过将地震各向异性观测与最低地幔流的地球动力学预测相结合来阐明。